chmod



CHMOD(1)                    General Commands Manual                   CHMOD(1)


NAME

     chmod - change file modes


SYNOPSIS

     chmod [-R [-H | -L | -P]] mode file ...


DESCRIPTION

     The chmod utility modifies the file mode bits of the listed files as
     specified by the mode operand.  The mode of a file dictates its
     permissions, among other attributes.

     The options are as follows:

     -H      If the -R option is also specified, symbolic links on the command
             line are followed.  Symbolic links encountered in the tree
             traversal are not followed.

     -L      If the -R option is also specified, all symbolic links are
             followed.

     -P      If the -R option is also specified, no symbolic links are
             followed.

     -R      Recurse.  Where file is a directory, change the mode of the
             directory and all the files and directories in the file hierarchy
             below it.

     Symbolic links have modes, but those modes have no effect on the kernel's
     access checks.  The -H, -L, and -P options are ignored unless the -R
     option is specified; if none of them are given, the default is to not
     follow symbolic links.  In addition, these options override each other
     and the command's actions are determined by the last one specified.

     Only the file's owner or the superuser is permitted to change the mode of
     a file.

   Absolute modes
     Absolute modes are specified according to the following format:

           chmod nnnn file ...

     An absolute mode is an octal number (specified as nnnn, where n is a
     number from 0 to 7) constructed by ORing any of the following values:

           0400    Allow read by owner.
           0200    Allow write by owner.
           0100    Allow execution (or search in directories) by owner.
           0700    Allow read, write, and execute/search by owner.
           0040    Allow read by group.
           0020    Allow write by group.
           0010    Allow execution (or search in directories) by group.
           0070    Allow read, write, and execute/search by group.
           0004    Allow read by others.
           0002    Allow write by others.
           0001    Allow execution (or search in directories) by others.
           0007    Allow read, write, and execute/search by others.

     In addition to the file permission modes, the following mode bits are
     available:

           4000    Set-user-ID on execution.
           2000    Set-group-ID on execution.
           1000    Enable sticky bit; see sticky(8) and chmod(2).

     The execute bit for a directory is often referred to as the ``search''
     bit.  In order to access a file, a user must have execute permission in
     each directory leading up to it in the filesystem hierarchy.  For
     example, to access the file /bin/ls, execute permission is needed on /,
     /bin, and, of course, the ls binary itself.

   Symbolic modes
     Symbolic modes are specified according to the following format:

           chmod [who]op[perm],... file ...

     The who symbols indicate whose permissions are to be changed or assigned:

           u     User (owner) permissions.
           g     Group permissions.
           o     Others permissions.
           a     All of the above.

     Do not confuse the `o' symbol with ``owner''.  It is the user bit, `u',
     that refers to the owner of the file.

     The op symbols represent the operation performed, as follows:

           +     If no value is supplied for perm, the `+' operation has no
                 effect.  If no value is supplied for who, each permission bit
                 specified in perm, for which the corresponding bit in the
                 file mode creation mask is clear, is set.  Otherwise, the
                 mode bits represented by the specified who and perm values
                 are set.

           -     If no value is supplied for perm, the `-' operation has no
                 effect.  If no value is supplied for who, each permission bit
                 specified in perm, for which the corresponding bit in the
                 file mode creation mask is clear, is cleared.  Otherwise, the
                 mode bits represented by the specified who and perm values
                 are cleared.

           =     The mode bits specified by the who value are cleared, or, if
                 no who value is specified, the user, group and other mode
                 bits are cleared.  Then, if no value is supplied for who,
                 each permission bit specified in perm, for which the
                 corresponding bit in the file mode creation mask is clear, is
                 set.  Otherwise, the mode bits represented by the specified
                 who and perm values are set.

     The perm (permission symbols) represent the portions of the mode bits as
     follows:

           r       Read bits.
           s       Set-user-ID and set-group-ID on execution bits.
           t       Sticky bit.
           w       Write bits.
           x       Execute/search bits.
           X       The execute/search bits if the file is a directory or any
                   of the execute/search bits are set in the original
                   (unmodified) mode.  Operations with the perm symbol `X' are
                   only meaningful in conjunction with the op symbol `+', and
                   are ignored in all other cases.
           u       User permission bits in the mode of the original file.
           g       Group permission bits in the mode of the original file.
           o       Other permission bits in the mode of the original file.

     Each clause (given in a comma-delimited list on the command line)
     specifies one or more operations to be performed on the mode bits, and
     each operation is applied in the order specified.

     Operations upon the ``other'' permissions (specified by the symbol `o' by
     itself), in combination with the perm symbols `s' or `t', are ignored.


EXIT STATUS

     The chmod utility exits 0 on success, and >0 if an error occurs.


EXAMPLES

     Set file readable by anyone and writable by the owner only:

           $ chmod 644 file

     Deny write permission to group and others:

           $ chmod go-w file

     Set the read and write permissions to the usual defaults, but retain any
     execute permissions that are currently set:

           $ chmod =rw,+X file

     Make a directory or file searchable/executable by everyone if it is
     already searchable/executable by anyone:

           $ chmod +X file

     Any of these commands will make a file readable/executable by everyone
     and writable by the owner only:

           $ chmod 755 file
           $ chmod u=rwx,go=rx file
           $ chmod u=rwx,go=u-w file

     Clear all mode bits for group and others:

           $ chmod go= file

     Set the group bits equal to the user bits, but clear the group write bit:

           $ chmod g=u-w file


SEE ALSO

     chflags(1), chgrp(1), find(1), install(1), chmod(2), stat(2), umask(2),
     fts(3), setmode(3), symlink(7), chown(8), sticky(8)


STANDARDS

     The chmod utility is compliant with the IEEE Std 1003.1-2008
     (``POSIX.1'') specification.

     The flags [-HLP] are extensions to that specification.

     The `t' perm symbol (sticky bit) is marked by IEEE Std 1003.1-2008
     (``POSIX.1'') as being an X/Open System Interfaces option.


HISTORY

     A chmod command appeared in Version 1 AT&T UNIX.


BUGS

     There's no perm option for the naughty bits.

OpenBSD 5.7                    December 13, 2014                   OpenBSD 5.7

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